This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 1/29/2008 This is a multi-center, 1:1 randomized, double-blind, placebo-controlled, through the 5 gm Oral Food Challenge (OFC) at week 44, trial to investigate the safety and immunologic effects of daily peanut sublingual immunotherapy (SLIT) for peanut allergy. The primary objective is to determine in subjects with peanut allergy whether daily sublingual administration of peanut protein induces increased peanut desensitization as measured by OFCs after 44 weeks of therapy and after a total maintenance SLIT therapy of approximately 1, 2, and 3 years. The secondary objectives are as follows: 1.) To determine the percentage of subjects who tolerate the buildup stage to 2100 mcg/day of peanut SLIT. 2.) To determine if "higher-dose" peanut SLIT (3500 mcg daily maintenance of peanut protein), compared to the initial dose peanut SLIT (2100 mcg daily maintenance of peanut protein), results in the development of differences in desensitization to peanut as determined by OFC. 3.) To determine if, after approximately 36 months of maintenance peanut SLIT, the peanut desensitization and changes in immunologic parameters are sustainable ["tolerance" induction] once daily therapy is discontinued for 8 weeks and functional tolerance occurs. 4.) To characterize the safety of peanut SLIT by determining the incidence of all serious adverse events throughout the duration of the study. Hypothesis: Daily ingestion of small amounts of peanut protein will desensitize peanut-allergic individuals (increasing their ability to ingest peanut while on therapy) and after long term treatment will induce tolerance to peanut (a permanent ability to ingest peanut while off therapy).